data: preMildFull and postMildFull
t = 5.9208, df = 2365.1, p-value = 3.67e-09
alternative hypothesis: true difference in means is not equal to 0
95 percent confidence interval:
3.426408 6.820007
sample estimates:
mean of x mean of y
75.95418 70.83098
Judging from the number of degrees of freedom, you have two large samples, therefore your test is very sensitive. Even for a small effect size it will result in a small p-value and the test result will be 'significant'. P-value is less important here.
You need to look at the effect size (difference between the means, which is 5.1±1.7) and judge if it is important for your case of not. Without seeing the full data and understanding the case, it is hard to interpret your result.